La resiliencia escolar se construye a partir de las relaciones

The visualization of the solids phase separation in the CFB, by a high-speed video camera in combination with the image calibration method, is conducted in the fully developed region in a narrow rectangular CFB riser with a 19 mm×114 mm cross section and a 7.6 m height.

Using an image calibration method, the cross sectional solids holdup under different operating conditions can be calculated from the mean grayscale of the images. The results

2 4 6 8 10 12 14 0 20 40 60 80 100 cluster fraction (_sc = 0.04) cluster fraction (_sc = 0.08) _s

Superficial gas velocity (m/s)

Clust e r Fract ion (% ) 0.00 0.01 0.02 0.03 0.04 0.05 Mean solids holdup (  ) G_s = 100 kg/m2s

are consistent with the previous studies. The transformation from grayscale images into binary images using various solids holdup thresholds allows the solids holdup distribution to be clearly visualized along the lateral direction under different operating conditions in the fully developed region. At the same time, a term “relative dense phase area” is introduced to quantify the distribution of dilute and dense phases.

A critical solids holdup value of εsc = 0.04 is chosen to demarcate the dilute and cluster

phases, by finding the minimum first derivative of the variation profile of relative dense phase area with solids holdup thresholds. It is found that cluster fraction is in the range from 1 % to 59 % under the operating conditions in the present research. With images divided into three regions along the lateral direction: the core, the middle and the wall regions, cluster fraction is higher at the wall region than that of the core and middle regions, indicating that clusters are prone to form in the wall region than the other two. In addition, it is found that the cluster fraction depends on the cluster critical solids holdup. With different value selected, the cluster fraction is different.

Acknowledgements

The authors acknowledge with gratitude the financial support of the National Science and Engineering Research Council of Canada (NSERC) and the China Scholarship Council (CSC).

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